Systems and methods for depositing material onto microfeature workpieces in reaction chambers

ABSTRACT

Systems and methods for depositing material onto a microfeature workpiece in a reaction chamber are disclosed herein. In one embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The first valve assembly includes first and second valves that are in fluid communication with the first gas conduit. The first and second valves are configured in a parallel arrangement so that the first gas flows through the first valve and/or the second valve. It is emphasized that this Abstract is provided to comply with the rules requiring an abstract. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

TECHNICAL FIELD

The present invention is related to systems and methods for depositing material in thin film deposition processes used in the manufacturing of microfeatures.

BACKGROUND

Thin film deposition techniques are widely used in the manufacturing of microfeatures to form a coating on a workpiece that closely conforms to the surface topography. The size of the individual components in the workpiece is constantly decreasing, and the number of layers in the workpiece is increasing. As a result, both the density of components and the aspect ratios of depressions (i.e., the ratio of the depth to the size of the opening) are increasing. The size of workpieces is also increasing to provide more real estate for forming more dies (i.e., chips) on a single workpiece. Many fabricators, for example, are transitioning from 200 mm to 300 mm workpieces, and even larger workpieces will likely be used in the future. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms, and corners in deep depressions that have very small openings.

One widely used thin film deposition technique is Chemical Vapor Deposition (CVD). In a CVD system, one or more precursors that are capable of reacting to form a solid thin film are mixed while in a gaseous or vaporous state, and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes the reaction between the precursors to form a solid thin film at the workpiece surface. A common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction.

Although CVD techniques are useful in many applications, they also have several drawbacks. For example, if the precursors are not highly reactive, then a high workpiece temperature is needed to achieve a reasonable deposition rate. Such high temperatures are not typically desirable because heating the workpiece can be detrimental to the structures and other materials already formed on the workpiece. Implanted or doped materials, for example, can migrate within the silicon substrate at higher temperatures. On the other hand, if more reactive precursors are used so that the workpiece temperature can be lower, then reactions may occur prematurely in the gas phase before reaching the substrate. This is undesirable because the film quality and uniformity may suffer, and also because it limits the types of precursors that can be used.

Atomic Layer Deposition (ALD) is another thin film deposition technique. FIGS. 1A and 1B schematically illustrate the basic operation of ALD processes. Referring to FIG. 1A, a layer or partial layer of gas molecules A_(x) coats the surface of a workpiece W. The layer of A_(x) molecules is formed by exposing the workpiece W to a precursor gas containing A_(x) molecules and then purging the chamber with a purge gas to remove excess A_(x) molecules. This process can form a monolayer or partial monolayer of A_(x) molecules on the surface of the workpiece W because the A_(x) molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. Referring to FIG. 1B, the layer of A_(x) molecules is then exposed to another precursor gas containing B_(y) molecules. The A_(x) molecules react with the B_(y) molecules to form an extremely thin layer of solid material on the workpiece W. The chamber is then purged again with a purge gas to remove excess B_(y) molecules.

FIG. 2 illustrates the stages of one cycle for forming a thin solid layer using ALD techniques. A typical cycle includes (a) exposing the workpiece to the first precursor A_(x), (b) purging excess A_(x) molecules, (c) exposing the workpiece to the second precursor B_(y), and then (d) purging excess B_(y) molecules. In actual processing, several cycles are repeated to build a thin film on a workpiece having the desired thickness. For example, each cycle may form a layer or partial layer having a thickness of approximately 0.1-1.0 Å, and thus several cycles are required to form a solid layer having a thickness of approximately 60 Å.

FIG. 3 schematically illustrates a single-wafer ALD reactor 10 having a reaction chamber 20 coupled to a gas supply 30 and a vacuum 40. The reactor 10 also includes a heater 50 that supports the workpiece W and a gas dispenser 60 in the reaction chamber 20. The gas dispenser 60 includes a plenum 62 operably coupled to the gas supply 30 and a distributor plate 70 having a plurality of holes 72. In operation, the heater 50 heats the workpiece W to a desired temperature, and the gas supply 30 selectively injects the first precursor A_(x), the purge gas, and the second precursor B_(y), as shown above in FIG. 2. The vacuum 40 maintains a negative pressure in the chamber to draw the gases from the gas dispenser 60 across the workpiece W and then through an outlet of the reaction chamber 20.

One drawback of ALD processing is that it has a relatively low throughput compared to CVD techniques. For example, each A_(x)-purge-B_(y)-purge cycle can take several seconds. This results in a total process time of several minutes to form a single thin layer of only 60 Å. In contrast to ALD processing, CVD techniques require only about one minute to form a 60 Å thick layer. The low throughput of existing ALD techniques limits the utility of the technology in its current state because ALD may be a bottleneck in the overall manufacturing process.

Another drawback of ALD and pulsed CVD processing is the downtime required to service the valves that control the flow of precursor into the reaction chamber. The flow of each precursor is controlled B_(y) a single, quick-action valve that actuates at least once per cycle to provide the precursor to the gas dispenser. For example, the valves can actuate between 100-2000 times to build a single 200 Å thick layer. Accordingly, the high frequency of actuations causes the valves to wear out relatively quickly. Replacing and servicing these valves requires downtime, increases operating costs, and causes an associated reduction in throughput. Therefore, there is a significant need to reduce the downtime for servicing components in CVD and ALD reactors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views of stages in ALD processing in accordance with the prior art.

FIG. 2 is a graph illustrating a cycle for forming a layer using ALD techniques in accordance with the prior art.

FIG. 3 is a schematic representation of a system including a reactor for depositing material onto a microfeature workpiece in accordance with the prior art.

FIG. 4 is a schematic representation of a system for depositing material onto a microfeature workpiece in accordance with one embodiment of the invention.

FIG. 5 is a schematic isometric view of a valve assembly for use in the system shown in FIG. 4 in accordance with another embodiment of the invention.

FIG. 6 is a schematic side cross-sectional view of a valve assembly for use in the system shown in FIG. 4 in accordance with yet another embodiment of the invention.

DETAILED DESCRIPTION

A. Overview

The following disclosure describes several embodiments of systems and methods for depositing material onto microfeature workpieces in reaction chambers. Many specific details of the invention are described below with reference to single-wafer reactors for depositing material onto microfeature workpieces, but several embodiments can be used in batch systems for processing a plurality of workpieces simultaneously. The term “microfeature workpiece” is used throughout to include substrates upon which and/or in which microelectronic devices, micromechanical devices, data storage elements, read/write components, and other features are fabricated. For example, microfeature workpieces can be semiconductor wafers such as silicon or gallium arsenide wafers, glass substrates, insulative substrates, and many other types of materials. Furthermore, the term “gas” is used throughout to include any form of matter that has no fixed shape and will conform in volume to the space available, which specifically includes vapors (i.e., a gas having a temperature less than the critical temperature so that it may be liquefied or solidified by compression at a constant temperature). Several embodiments in accordance with the invention are set forth in FIGS. 4-6 and the following text to provide a thorough understanding of particular embodiments of the invention. A person skilled in the art will understand, however, that the invention may have additional embodiments, or that the invention may be practiced without several of the details of the embodiments shown in FIGS. 4-6.

One aspect of the invention is directed to a system for depositing material onto a microfeature workpiece in a reaction chamber. In one embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The first valve assembly includes first and second valves that are in fluid communication with the first gas conduit. The first and second valves are configured in a parallel arrangement so that the first gas flows through the first valve and/or the second valve.

In one aspect of this embodiment, the system further includes a controller configured to operate the first and second valves simultaneously or in an alternating sequence. In another aspect of this embodiment, the first valve assembly further includes first and second gas passageways in fluid communication with the first gas conduit. The first valve can be configured to control the first gas flow through the first passageway, and the second valve can be configured to control the first gas flow through the second passageway. In another aspect of this embodiment, the first valve assembly further includes a third valve in fluid communication with the first gas conduit. The first, second, and third valves can be arranged symmetrically so that the first, second, and third valves are spaced apart from a portion of the gas distributor by at least approximately the same distance.

In another embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a first valve and a second valve each in fluid communication with the first gas conduit, a reaction chamber, and a gas distributor carried by the reaction chamber. The first and second valves are operable independently to individually and/or jointly provide pulses of the first gas downstream from the first and second valves. The gas distributor is in fluid communication with the first and second valves to receive the pulses of the first gas.

In another embodiment, the system includes a gas supply assembly having a first gas source, a first gas conduit coupled to the first gas source, a valve assembly, a reaction chamber, and a gas distributor carried by the reaction chamber. The valve assembly includes a body with first and second gas passageways, a first valve stem configured to control the flow of the first gas through the first gas passageway, and a second valve stem configured to control the flow of the first gas through the second gas passageway. The first and second gas passageways are in fluid communication with the first gas conduit and are configured in a parallel arrangement.

Another aspect of the invention is directed to a method of depositing material onto a microfeature workpiece in a reaction chamber. In one embodiment, the method includes flowing a first pulse of a first gas through a first gas conduit and a first valve into the reaction chamber. The method further includes flowing a second pulse of the first gas through the first gas conduit and a second valve into the reaction chamber without flowing the second pulse of the first gas through the first valve. In one aspect of this embodiment, flowing the first pulse of the first gas includes controlling the first valve to dispense the first pulse of the first gas into the reaction chamber, and flowing the second pulse of the first gas includes controlling the second valve to dispense the second pulse of the first gas into the reaction chamber.

B. Deposition Systems

FIG. 4 is a schematic representation of a system 100 for depositing material onto a microfeature workpiece W in accordance with one embodiment of the invention. In this embodiment, the system 100 includes a reactor 110 having a reaction chamber 120 coupled to a gas supply 130 and a vacuum 140. The reactor 110 also includes a gas distributor 160 coupled to the reaction chamber 120 and the gas supply 130 to dispense gas(es) into the reaction chamber 120 and onto the workpiece W.

The gas supply 130 includes a plurality of gas sources 132 (identified individually as 132 a-c) and a plurality of upstream main lines 136 coupled to the gas sources 132. The gas sources 132 can include a first gas source 132 a for providing a first gas, a second gas source 132 b for providing a second gas, and a third gas source 132 c for providing a third gas. The first and second gases can be first and second precursors, respectively. The third gas can be a purge gas. The first and second precursors are the gas and/or vapor phase constituents that react to form the thin, solid layer on the workpiece W. The purge gas can be a suitable type of gas that is compatible with the reaction chamber 120 and the workpiece W. In other embodiments, the gas supply 130 can include a different number of gas sources 132 for applications that require additional precursors or purge gases. In additional embodiments, the gas sources 132 can include one or more etchants for deposition onto a microfeature workpiece during etching.

In the illustrated embodiment, the reactor 110 also includes a workpiece support 150 to hold the workpiece W in the reaction chamber 120. In one aspect of this embodiment, the workpiece support 150 can be heated to bring the workpiece W to a desired temperature for catalyzing the reaction between the first gas and the second gas at the surface of the workpiece W. For example, the workpiece support 150 can be a plate with a heating element. The workpiece support 150, however, may not be heated in other applications.

The system 100 of the illustrated embodiment further includes a plurality of valve assemblies 168 (identified individually as 168 a-c) coupled to the upstream main lines 136 and a plurality of downstream main lines 139 coupled to the valve assemblies 168 and the gas distributor 160. The valve assemblies 168 can include a plurality of branch lines 137 (identified individually as 137 a-b) attached to the upstream and downstream main lines 136 and 139 and a plurality of valves 170 (identified individually as 170 a-b) attached to the branch lines 137. The branch lines 137 flow the gases from the upstream main lines 136 to the downstream main lines 139, and the valves 170 control the flow of the gases through the branch lines 137. In the illustrated embodiment, the first and second valves 170 a-b are configured in a parallel arrangement, and accordingly, each portion of gas flows through either the first valve 170 a or the second valve 170 b of the corresponding valve assembly 168. In other embodiments, such as those described below with reference to FIGS. 5 and 6, the valve assemblies can have a different configuration and/or a different number of valves. For example, several valve assemblies 168 can be combined into a single valve assembly, and/or the valve assemblies 168 can be carried by the reaction chamber 120.

The valve assemblies 168 are operated by a controller 142 that generates signals for controlling the flow of gases into the reaction chamber 120 for ALD and CVD applications. For example, the controller 142 can be programmed to operate the valve assemblies 168 to pulse the gases individually through the gas distributor 160 in ALD applications or mix selected precursors in the gas distributor 160 in CVD applications. More specifically, in one embodiment of an ALD process, the controller 142 actuates the first valve 170 a of a first valve assembly 168 a to dispense a pulse of the first gas (e.g., the first precursor) into the reaction chamber 120. Next, the controller 142 actuates the first valve 170 a of a third valve assembly 168 c to dispense a pulse of the third gas (e.g., the purge gas) into the reaction chamber 120. The controller 142 then actuates the first valve 170 a of a second valve assembly 168 b to dispense a pulse of the second gas (e.g., the second precursor) into the reaction chamber 120. Next, the controller 142 actuates the second valve 170 b of the third valve assembly 168 c to dispense a pulse of the third gas into the reaction chamber 120. In the next cycle, the process is repeated except the controller 142 actuates the second valves 170 b (rather than the first valves 170 a) of the first and second valve assemblies 168 a-b to dispense pulses of the first and second gases into the reaction chamber 120.

In one embodiment of a pulsed CVD process, the controller 142 actuates the first valves 170 a of the first and second valve assemblies 168 a-b to dispense a pulse of the first and second gases (e.g., the first and second precursors) into the reaction chamber 120. Next, the controller 142 actuates the first valve 170 a of the third valve assembly 168 c to dispense a pulse of the third gas (e.g., the purge gas) into the reaction chamber 120. In the next cycle, the controller 142 actuates the second valves 170 b (rather than the first valves 170 a) of the first and second valve assemblies 168 a-b to dispense a pulse of the first and second gases into the reaction chamber 120. The controller 142 then actuates the second valve 170 b of the third valve assembly 168 c to dispense a pulse of the third gas into the reaction chamber 120. In other embodiments, the controller 142 can actuate the valves 170 in other sequences.

One feature of the illustrated embodiment is that each gas source is coupled to a valve assembly with a plurality of valves. By coupling several valves to each gas source, the frequency with which each valve is actuated to dispense gas is reduced. For example, if each gas source is coupled to a valve assembly with two valves, the frequency that each valve is actuated may be reduced by one half. One advantage of this feature is that the life of the valve assembly is extended because the valves do not wear out as quickly. When the valves wear out or otherwise fail, the system is shut down to replace and/or service the valves. Accordingly, the system of the illustrated embodiment reduces the downtime to replace and/or service the valves and thereby increases the throughput.

In other embodiments, the controller 142 can simultaneously actuate the first and second valves 170 a-b of a single valve assembly 168 to dispense a portion of the corresponding gas into the reaction chamber 120. One advantage of this arrangement is that if one valve fails, the other valve in the valve assembly will continue to dispense gas for deposition onto the workpiece W.

C. Other Valve Assemblies

FIG. 5 is a schematic isometric view of a valve assembly 268 for use in the system 100 shown in FIG. 4 in accordance with another embodiment of the invention. The valve assembly 268 includes a plurality of valves 270 (identified individually as 270 a-c) and a plurality of branch lines 237 (identified individually as 237 a-c) coupling the valves 270 to the upstream and downstream main lines 136 and 139. In one aspect of this embodiment, the branch lines 237 and the valves 270 are arranged symmetrically so that the valves 270 provide pulses of gas to the reaction chamber 120 (FIG. 4) at a consistent pressure and with a consistent response time. For example, the branch lines 237 can include a first portion 243 coupled to the upstream main line 136, a second portion 244 coupled to the first portion 243 and the valve 270, a third portion 245 coupled to the valve 270, and a fourth portion 246 coupled to the third portion 245 and the downstream main line 139. The first portions 243 can be oriented at generally the same angle relative to the upstream main line 136, and the fourth portions 246 can be oriented at generally the same angle relative to the downstream main line 139. The second and third portions 244 and 245 can be generally parallel to the upstream and downstream main lines 136 and 139. Moreover, the portions 243, 244, 245 and 246 in each branch line 237 can have approximately the same length as the corresponding portions in the other branch lines 237. In this embodiment, the symmetric arrangement can ensure that each valve 270 provides consistent and uniform pulses of gas to the reaction chamber 120 (FIG. 4). In other embodiments, the valve assembly 268 may have other configurations, including asymmetric arrangements. For example, the valve assembly can include a body with gas passageways, such as in the embodiment described below with reference to FIG. 6, or the valve assembly can include a different number of valves.

FIG. 6 is a schematic side cross-sectional view of a valve assembly 368 for use in the system 100 shown in FIG. 4 in accordance with another embodiment of the invention. The valve assembly 368 includes a valve body 372 having a first gas passageway 338 a and a second gas passageway 338 b, a first valve stem 380 a in the valve body 372, and a second valve stem 380 b in the valve body 372. The valve body 372 includes an inlet 374 configured for attachment to the upstream main line 136 (FIG. 4), an outlet 376 configured for attachment to the downstream main line 139 (FIG. 4), a plurality of valve seats 383, and a plurality of cavities 378. The first and second valve stems 380 a-b include a first portion 381 configured to engage the valve seat 383 and a second portion 382 configured to be received in the cavity 378. The first and second valve stems 380 a-b are movable in a direction D between a first position (illustrated by the first valve stem 380 a) in which the first portion 381 engages the valve seat 383 and a second position (illustrated by the second valve stem 380 b) in which the second portion 382 is received in the cavity 378. The position of the first and second valve stems 380 a-b controls the flow of gas through the gas passageways 338.

In operation, a gas flow “F” enters the valve body 372 through the inlet 374 and is split into two separate flows at a junction 347 of the first and second gas passageways 338 a-b. The first and second gas passageways 338 a-b are configured in a parallel arrangement so that each portion of gas flows through either the first gas passageway 338 a or the second gas passageway 338 b. When one or both of the valve stems 380 a-b are in the second position, the gas flows past the valve stems 380 a-b and exits the valve body 372 through the outlet 376. In one embodiment, a controller can actuate the valve stems 380 in an alternating sequence so that when one valve stem 380 is in the second position, the other valve stem 380 is in the first position. In other embodiments, a controller can actuate the valve stems 380 simultaneously so that both of the valve stems 380 can be in the second position at the same time. In additional embodiments, the valve assembly 368 can include a different number of valve stems 380 and gas passageways 338. For example, a valve assembly can include four gas passageways and four valve stems.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited, except as by the appended claims. 

1. A system for depositing material onto a microfeature workpiece in a reaction chamber, the system comprising: a gas supply assembly having a first gas source for containing a first gas; a first gas conduit coupled to the first gas source; a first valve assembly including first and second valves in fluid communication with the first gas conduit, the first and second valves configured in a parallel arrangement so that the first gas flows through the first valve and/or the second valve; a reaction chamber; and a gas distributor carried by the reaction chamber and in fluid communication with the first valve assembly.
 2. The system of claim 1, further comprising a controller configured to operate the first and second valves in an alternating sequence.
 3. The system of claim 1, further comprising a controller configured to operate the first and second valves at least partially simultaneously.
 4. The system of claim 1 wherein the first valve assembly further comprises first and second gas passageways in fluid communication with the first gas conduit, the first valve being configured to control the first gas flow through the first passageway, and the second valve being configured to control the first gas flow through the second passageway.
 5. The system of claim 1 wherein the first valve assembly further comprises a third valve in fluid communication with the first gas conduit, the first, second, and third valves being arranged symmetrically so that the first, second, and third valves are spaced apart from a portion of the gas distributor by at least approximately the same distance.
 6. The system of claim 1 wherein the gas supply assembly further comprises a second gas source for containing a second gas, and wherein the system further comprises: a second gas conduit coupled to the second gas source and in fluid communication with the gas distributor; and a second valve assembly including third and fourth valves in fluid communication with the second gas conduit, the third and fourth valves being configured in a parallel arrangement so that the second gas flows through the third valve and/or the fourth valve.
 7. A system for depositing material onto a microfeature workpiece in a reaction chamber, the system comprising: a gas supply assembly having a first gas source containing a first gas; a first gas conduit coupled to the first gas source; a first valve and a second valve each in fluid communication with the first gas conduit, the first and second valves being operable independently to individually and/or jointly provide pulses of the first gas downstream from the first and second valves; a reaction chamber; and a gas distributor carried by the reaction chamber and in fluid communication with the first and second valves to receive the pulses of the first gas.
 8. The system of claim 7, further comprising a controller configured to operate the first and second valves in an alternating sequence.
 9. The system of claim 7, further comprising a controller configured to operate the first and second valves simultaneously.
 10. The system of claim 7, further comprising first and second gas passageways coupled to the first gas conduit, the first valve configured to control the first gas flow through the first passageway, and the second valve configured to control the first gas flow through the second passageway.
 11. The system of claim 7, further comprising a third valve in fluid communication with the first gas conduit, the first, second, and third valves being arranged symmetrically so that the first, second, and third valves are spaced apart from a portion of the gas distributor by at least approximately the same distance.
 12. The system of claim 7 wherein the gas supply assembly further comprises a second gas source for containing a second gas, and wherein the system further comprises: a second gas conduit coupled to the second gas source and in fluid communication with the gas distributor; and a third valve and a fourth valve each in fluid communication with the second gas conduit, the third and fourth valves being operable independently to individually and/or jointly provide pulses of the second gas downstream from the third and fourth valves.
 13. A system for depositing material onto a microfeature workpiece in a reaction chamber, the system comprising: a gas supply assembly having a first gas source for providing a first gas; a first gas conduit coupled to the first gas source to carry the first gas from the first gas source; a valve assembly including a body with first and second gas passageways in fluid communication with the first gas conduit, a first valve stem configured to control the flow of the first gas through the first gas passageway, and a second valve stem configured to control the flow of the first gas through the second gas passageway, the first and second gas passageways configured in a parallel arrangement; a reaction chamber; and a gas distributor carried by the reaction chamber and in fluid communication with the first gas conduit.
 14. The system of claim 13, further comprising a controller configured to operate the first and second valve stems in an alternating sequence.
 15. The system of claim 13, further comprising a controller configured to operate the first and second valve stems simultaneously.
 16. The system of claim 13 wherein: the body of the valve assembly further comprises a third gas passageway in fluid communication with the first gas conduit; and the valve assembly further comprises a third valve stem configured to control the flow of the first gas through the third gas passageway.
 17. The system of claim 13 wherein: the valve assembly comprises a first valve assembly; the body comprises a first body; the gas supply assembly further comprises a second gas source for providing a second gas; and the system further comprises— a second gas conduit coupled to the second gas source and in fluid communication with the gas distributor; and a second valve assembly including a second body having third and fourth gas passageways in fluid communication with the second gas conduit, a third valve stem configured to control the flow of the second gas through the third gas passageway, and a fourth valve stem configured to control the flow of the second gas through the fourth gas passageway, the third and fourth gas passageways configured in a parallel arrangement.
 18. A method of depositing material onto a microfeature workpiece in a reaction chamber, the method comprising: flowing a first pulse of a first gas through a first gas conduit and a first valve into the reaction chamber; and flowing a second pulse of the first gas through the first gas conduit and a second valve into the reaction chamber without flowing the second pulse of the first gas through the first valve.
 19. The method of claim 18 wherein flowing the second pulse of the first gas occurs after flowing the first pulse of the first gas.
 20. The method of claim 18 wherein the procedures of flowing the first pulse of the first gas and flowing the second pulse of the first gas are repeated sequentially.
 21. The method of claim 18 wherein the procedures of flowing the first pulse and flowing the second pulse occur at least partially simultaneously.
 22. The method of claim 18 wherein: flowing the first pulse of the first gas comprises controlling the first valve to dispense the first pulse of the first gas into the reaction chamber; and flowing the second pulse of the first gas comprises controlling the second valve to dispense the second pulse of the first gas into the reaction chamber.
 23. The method of claim 18 wherein: the first and second valves are configured in a parallel arrangement; and flowing the first and second pulses of the first gas comprise flowing the first and second pulses of the first gas through the first and second valves configured in the parallel arrangement.
 24. The method of claim 18 wherein: the first and second valves are part of a valve assembly; flowing the first pulse of the first gas through the first valve comprises flowing the first pulse of the first gas through the valve assembly; and flowing the second pulse of the first gas through the second valve comprises flowing the second pulse of the first gas through the valve assembly.
 25. The method of claim 18 wherein: flowing the first pulse of the first gas comprises flowing the first pulse of the first gas through a first gas passageway; and flowing the second pulse of the first gas comprises flowing the second pulse of the first gas through a second gas passageway, the first and second gas passageways being configured in a parallel arrangement.
 26. The method of claim 18, further comprising flowing a third pulse of the first gas through the first gas conduit and a third valve into the reaction chamber.
 27. The method of claim 18, further comprising: flowing a first pulse of a second gas through a second gas conduit and a third valve into the reaction chamber; and flowing a second pulse of the second gas through the second gas conduit and a fourth valve into the reaction chamber without flowing the second pulse of the second gas through the third valve.
 28. A method of depositing material onto a microfeature workpiece in a reaction chamber, the method comprising: controlling a first valve to provide a first pulse of a first gas to the reaction chamber through a first gas line independent of a second valve; and controlling the second valve to provide a second pulse of the first gas to the reaction chamber through the first gas line independent of the first valve.
 29. The method of claim 28 wherein: controlling the first valve comprises dispensing the first pulse of the first gas into the reaction chamber; and controlling the second valve comprises dispensing the second pulse of the first gas into the reaction chamber after dispensing the first pulse.
 30. The method of claim 28 wherein: controlling the first valve comprises flowing the first pulse of the first gas through a first gas passageway; controlling the second valve comprises flowing the second pulse of the first gas through a second gas passageway, the first and second gas passageways being configured in a parallel arrangement.
 31. The method of claim 28 wherein: the first and second valves are part of a valve assembly; controlling the first valve comprises controlling the first valve of the valve assembly; and controlling the second valve comprises controlling the second valve of the valve assembly.
 32. The method of claim 28, further comprising: controlling a third valve to provide a first pulse of a second gas to the reaction chamber through a second gas line; and controlling a fourth valve to provide a second pulse of the second gas to the reaction chamber through the second gas line independent of the third valve.
 33. A method for depositing material onto a microfeature workpiece in a reaction chamber, the method comprising: flowing a first pulse of a first gas through a first gas passageway in a valve assembly coupled to the reaction chamber; and flowing a second pulse of the first gas through a second gas passageway in the valve assembly, wherein the first and second gas passageways are configured in a parallel arrangement and are in fluid communication with a first gas conduit.
 34. The method of claim 33 wherein: flowing the first pulse of the first gas comprises controlling the flow of the first gas through the first passageway with a first valve stem; and flowing the second pulse of the first gas comprises controlling the flow of the first gas through the second passageway with a second valve stem.
 35. The method of claim 33, further comprising: flowing a third pulse of the first gas through a third gas passageway in the valve assembly; and flowing a fourth pulse of the first gas through a fourth gas passageway in the valve assembly, wherein the third and fourth gas passageways are configured in a parallel arrangement with the first and second gas passageways and are in fluid communication with the first gas conduit.
 36. A method for depositing material onto a microfeature workpiece in a reaction chamber, the method comprising: opening a first valve to dispense a first pulse of a first gas into the reaction chamber through a first downstream main line; closing the first valve; opening a second valve to dispense a second pulse of the first gas into the reaction chamber through the first downstream main line; and closing the second valve, wherein the first pulse of the first gas does not pass through the second valve and the second pulse of the first gas does not pass through the first valve.
 37. The method of claim 36, further comprising: opening a third valve to dispense a first pulse of a second gas into the reaction chamber through a second downstream main line; closing the third valve; opening a fourth valve to dispense a second pulse of the second gas into the reaction chamber through the second downstream main line; and closing the fourth valve, wherein the first pulse of the second gas does not pass through the fourth valve and the second pulse of the second gas does not pass through the third valve.
 38. The method of claim 36 wherein closing the first valve occurs before opening the second valve.
 39. The method of claim 36, further comprising: opening a third valve to dispense a third pulse of the first gas into the reaction chamber through the first downstream main line after closing the second valve; and closing the third valve. 